This invention relates generally to helicopter and rotor/wing aircraft and more specifically to such aircraft having reaction drive rotor blades.
Conventional helicopter aircraft typically comprise a plurality of rotor blades attached to a rotor at the top of the helicopter fuselage. The rotor is supported by a main shaft that is driven by a prime mover such as a conventional gas turbine engine operating through a transmission. The transmission typically comprises multiple stages of gears necessary to reduce the high speed low torque shaft output of the turbine engine into a low speed high torque shaft output necessary to drive the rotor. The weight associated with the transmission of a conventional helicopter limits the total payload achievable by conventional helicopters. This is especially true in the case of large, heavy lift helicopters. Moreover, the torque reaction caused by the rotor blades against the main shaft necessitates a substantial tail rotor or tail thruster to provide the antitorque control necessary to maintain the yaw attitude of a conventional helicopter, which also reduces fuel efficiency and the total power available to carry payload.
Accordingly, it has been suggested that the overall efficiency of very large helicopters and especially dual mode rotor/wing aircraft that fly predominantly in a fixed wing mode (such as the rotor/wing aircraft disclosed in U.S. Pat. No. 5,454,530, incorporated herein by reference) may be improved through the use of a reaction drive mechanism to drive the main rotor of such aircraft. In a preferred embodiment of a reaction drive mechanism, a flow of exhaust and/or bypass gases from a turbine engine are ducted through the rotor blades to exit from one or more nozzles at the trailing edges of the blade tips. Because the blades are caused to rotate about the fuselage by the mass flow rate of the exhaust gases exiting the blade tips, rather than by the exertion of a torque about the rotor main shaft, very little antitorque control is needed to maintain the yaw attitude of the aircraft.
As may be ascertained from the foregoing, because the primary lift mechanism of a reaction drive helicopter involves the ducting of the main engine exhaust from the main engine, through the rotor and into the rotor blades, it is imperative that the ducting be as short and smooth as possible and as free of bends and abrupt entrances and exits so as to minimize the pressure losses associated with the internal flow through the ducting.